The general aim of this program is to discover and clarify cellular mechanisms of Ca2+ homeostasis, as they relate to control of contractile tension and relaxation in cardiac muscle. Members of the departments of Biochemistry, Physiology and Medicine will combine their efforts, using mostly methods of Molecular and Cell Biology for this research. Project (Inesi) will study the sarcoplasmic reticulum (SR) ATPase, with regards to the molecular mechanism of ATP utilization for Ca2+ transport, the highly specific inhibition by thapsigargin, the effects of site directed mutations and the technology of gene transfer for expression of functional ATPase in various cells and cardiac muscle. Project (Rogers and lederer) will study the complementary functions of SR ATPase and Ryanodine Receptor channel in cardiac myocytes, as well as the modulatory effects of phosphorylation, using an integrated strategy of biochemistry, gene transfection, single cell voltage clamp and high resolution confocal Ca2+ imaging. Project (Hussain) will study the adaptation of Ca2+ hemostasis and the regulation of SR ATPase inhibitors such as thapsigargin and di- butyl-hydroquinone. The final Project (Wade) will utilize genetic methods to study the differential regulation of Troponin I isoform genes during heart development and maturation, identify separate elements involved in this regulation, and uncover the functional consequences of troponin I gene switching on the Ca2+ dependence of myofilaments activation. The four projects will interact with planned research collaborations and technical exchange. In addition Core A will provide Microscopy, Cell Culture and Recombinant DNA assistance to all projects. Core B will provide administrative support.